Adhesive-bonded thermal interface structures for integrated circuit cooling

ABSTRACT

A heat sink can be attached to a heat-producing electronic device by aligning an adhesive material to a surface of the heat sink, applying the adhesive material to the surface to form an outer perimeter and applying, within the outer perimeter, a thermally conductive material to the surface. The surface of the heat sink and a surface of the heat-producing electronic device can then be aligned, and the heat sink can be assembled to the heat-producing electronic device by bringing the heat-producing electronic device surface into contact with the adhesive material. The heat sink can then be affixed to the heat-producing electronic device by applying a compressive force to the assembly to activate the adhesive material.

BACKGROUND

This application claims priority to U.S. patent application Ser. No.15/629,171 filed on Jun. 21, 2017 and all the benefits accruingtherefrom, the contents of which are herein incorporated by reference.

A thermal interface material (TIM) can be used to enhance heat transfer,through reducing the thermal resistance between an electronic devicesuch as an integrated circuit (IC) and a heat sink. Types of TIMs caninclude, but are not limited to, thermal greases, adhesives, pads andgap fillers. TIMs can include thermally conductive solids andparticulate fillers which can be mixed with a binding agent such as asilicone or polymer compounds. A TIM can enhance thermal conductivity byfilling irregularities and air gaps between adjacent, mating surfaces,for example, of the IC and the heat sink, with a thermally conductivematerial.

A heat sink may be used in computers and electronic systems as a passiveheat exchanger, and may act as a reservoir that can absorb an arbitraryamount of heat without significantly changing temperature. Heat sinksmay be used in computers, for example, to cool devices such as centralprocessing units (CPUs) and/or graphics processing units (GPUs). Heatdissipation from a heat sink can be accomplished through convection,radiation, or conduction, into an ambient or circulated medium, such asair, water, or a coolant/refrigerant. Heat sinks reach a temperaturegreater than a cooling medium, in order to transfer heat across athermal gradient from an electronic device to the medium.

SUMMARY

Embodiments may be directed towards a method for attaching a heat sinkto a heat-producing electronic device. One of the heat sink and theheat-producing electronic device may have a first surface, the other ofthe heat sink and the heat-producing electronic device may have a secondsurface. The method can include aligning an adhesive material to thefirst surface and applying the adhesive material to the first surface toform an outer perimeter. The method can also include applying, withinthe outer perimeter, a thermally conductive material to the firstsurface, aligning the second surface to the first surface, andassembling the heat sink to the heat-producing electronic device bybringing the second surface into contact with the adhesive material. Themethod can also include affixing the heat sink to the heat-producingelectronic device by applying a compressive force to the heat sink andto the heat-producing electronic device, the compressive forceactivating the adhesive material.

Embodiments may also be directed towards an apparatus for cooling aheat-producing electronic device. The apparatus can include a heat sinkwith a first surface having a protrusion extending away from the firstsurface, the protrusion defining an inner perimeter on the firstsurface. The apparatus can also include an adhesive material affixed tothe first surface and to a second surface of the heat-producingelectronic device. The adhesive material can hold the first surface ofthe heat sink in an adjacent, coplanar orientation to the second surfaceof the heat-producing electronic device. The adhesive material candefine an outer perimeter on the first and second surfaces and form anouter cavity bounded by the outer perimeter, the first surface and thesecond surface. The apparatus can also include a thermally conductivematerial contained in an inner cavity enclosed within the outer cavity.The inner cavity can be bounded by the inner perimeter, the firstsurface and the second surface. The thermally conductive material can beconfigured to cool the heat-producing electronic device by providing athermally conductive path between the first surface and the secondsurface.

Embodiments may also be directed towards an apparatus for cooling aheat-producing electronic device. The apparatus can include a heat sinkhaving a first surface and an adhesive material affixed to the firstsurface and to a second surface of the heat-producing electronic device.The adhesive material can hold the first surface in an adjacent,coplanar orientation to the second surface. The adhesive material, in anunassembled configuration, can define a perimeter on the first andsecond surfaces and form a cavity bounded by the perimeter, the firstsurface and the second surface. The apparatus can also include a thermalinterface material (TIM) pad located within the cavity. The TIM pad canbe configured to cool the heat-producing electronic device by providinga thermally conductive path between the heat-producing electronic deviceand the heat sink. The thermally conductive path can include at least aportion of a third surface of the TIM pad in thermally conductivecontact with a corresponding portion of the first surface of the heatsink and at least a portion of a fourth surface of the TIM pad inthermally conductive contact with a corresponding portion of the secondsurface of the heat-producing electronic device.

The above summary is not intended to describe each illustratedembodiment or every implementation of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings included in the present application are incorporated into,and form part of, the specification. They illustrate embodiments of thepresent disclosure and, along with the description, serve to explain theprinciples of the disclosure. The drawings are only illustrative ofcertain embodiments and do not limit the disclosure.

FIG. 1 depicts an apparatus for cooling a heat-producing electronicdevice including a thermally conductive material enclosed within aninner perimeter of a heat sink, according to embodiments of the presentdisclosure.

FIG. 2 depicts an apparatus for cooling a heat-producing electronicdevice including a thermally conductive pad enclosed within a perimeter,according to embodiments consistent with the figures.

FIG. 3 depicts an apparatus for cooling a heat-producing electronicdevice including a thermally conductive pad and a thermally conductivematerial enclosed within a perimeter, according to embodimentsconsistent with the figures.

FIG. 4 depicts an apparatus for cooling a heat-producing electronicdevice including a thermally conductive pad and a thermally conductiveadhesive, according to embodiments consistent with the figures.

FIG. 5 includes a set of six consistent cross-sectional viewsillustrating the results of process operations for attaching a heat sinkto an electronic device, according to embodiments consistent with thefigures.

FIG. 6 is a flow diagram depicting a method for attaching a heat sink toan electronic device, according to embodiments consistent with thefigures.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention.

In the drawings and the Detailed Description, like numbers generallyrefer to like components, parts, steps, and processes.

DETAILED DESCRIPTION

Certain embodiments of the present disclosure can be appreciated in thecontext of providing efficient heat transfer between a heat-producingelectronic device and a heat sink for electronic equipment such asservers, which may be used to provide data to clients attached to aserver through a network. Such servers may include, but are not limitedto web servers, application servers, mail servers, and virtual servers.While not necessarily limited thereto, embodiments discussed in thiscontext can facilitate an understanding of various aspects of thedisclosure. Certain embodiments may also be directed towards otherequipment and associated applications, such as providing efficient heattransfer between a heat-producing electronic device and a heat sink forelectronic equipment such as computing systems, which may be used in awide variety of computational and data processing applications. Suchcomputing systems may include, but are not limited to, supercomputers,high-performance computing (HPC) systems, and other types ofspecial-purpose computers. Embodiments may also be directed towardsproviding efficient heat transfer between a heat-producing electronicdevice and a heat sink for electronic equipment such as desktopworkstations and computing systems, which can include heat-producingelectronic devices such as graphics processing units (GPUs).

The term “heat-producing electronic device” is used herein in referenceto devices such as one or more integrated circuits (ICs), and/or anelectronic module which can include one or more ICs or other electronicdevices. A heat-producing electronic device generates and dissipatesheat in response to electrical power consumed by the device. The terms“heat-producing electronic device” and “electronic device” are usedinterchangeably herein without loss of meaning.

For ease of discussion, the term “heat sink” is used herein withreference to various devices used to transfer and dissipate heatgenerated by heat-producing electronic devices. In the context of thepresent discussion, the term “heat sink” can refer to and include heatspreaders, heat pipe structures, and devices designed to dissipate heatinto cooling media such as ambient or circulated air, cooling liquid,e.g., water, or refrigerant.

The terms thermal interface material (“TIM”) and “TIM pad” are usedinterchangeably herein with reference to various commercially availablethermally conductive pads used to transfer heat from a heat-producingelectronic device to a heat sink. TIM pads can be fabricated from avariety of different thermally conductive materials, e.g., carbonfibers, indium, copper and silver. TIM pads can be used to enhancethermal conductivity by filling in gaps and surface irregularities foundon the mating surfaces of a heat-producing electronic device and a heatsink. TIM pads are generally thin, e.g., between 0.1 mm and 0.5 mmthick, pre-formed, and can be fragile. Various TIM pads can have a rangeof resiliency, in response to compressive forces, depending on thephysical properties of materials used to construct the TIM pad.

In the context of the present discussion, the terms “copper,” “aluminum”and “indium” and “silver” are used herein in reference to highlythermally conductive materials, such as metals, used in embodiments. Itcan be understood however that various embodiments can also be usefulwith regards to metallic alloys which may include copper, aluminum,indium, silver and/or other thermally conductive materials.

The trends of decreasing dimensions of ICs, e.g., processor chips, andincreasing IC power dissipation have generally occurred simultaneously,resulting in increased operating temperatures and power densities ofelectronic devices. These converging trends have highlighted theimportance of providing an efficient thermal interface between aheat-producing electronic device such as an IC or multi-IC electronicmodule and a cooling device such as a heat sink. Such an efficientthermal interface can be effective in maintaining the electronicdevice's operating temperature within a specified operating range.

In order for a thermal interface to be effective in transferring heatfrom a heat-producing electronic device, it may need to possess a numberof attributes. Such attributes can include high thermal conductivity,and the ability to fill surface irregularities/gaps betweenheat-producing electronic device and heat sink surfaces, while beingrelatively compliant and compressible under the application of arelatively low compression force. An effective thermal interface canalso be stable and reliable over time and/or repeated thermal cycles,and should not manifest “grease pumping” or thermal interface materialdisplacement/voiding resulting from electronic device and/or heat sinkthermally-induced flexing. A robust thermal interface can be durablewithin “shock and vibration” environments, and constructed frommaterials that are chemically inert with respect to each other. Adesirable thermal interface can have a relatively low-cost, simple andstraightforward implementation involving minimal surface preparationrequirements, processing/material handling issues, and may require nolatching hardware to attach the heat sink to the heat-producingelectronic device.

A number of materials can be used to construct a thermal interfacebetween a heat-producing electronic device and a heat sink. While eachof these materials can possess attributes beneficial to thermalinterface construction, each of them may also have characteristics thatcan contribute to the thermal interface's premature failure and/ordegrade its performance. For example, in some applications, thermalcompounds known as “thermal greases” can provide low-cost, high thermalconductivity gap filling for relatively large and/or variable gapsbetween a heat-producing electronic device and a heat sink. Thermalgreases can, however, be subject to “grease pumping” or displacementover time and/or a number of thermal cycles, which can significantlyreduce the effectiveness of the thermal interface. Thermal compoundsknown as “thermal gels” can provide robust gap-filling capability andhigh thermal conductivity; however, thermal gels can require complicatedand expensive surface preparations and material storage/handling inorder to ensure long-term material adhesion and thermal performance.Thermal gels can also be sensitive to degradation within “shock andvibration” environments. TIM pads can provide high thermal conductivityand be relatively easy to implement, however, TIM pads can also havelimited compressibility and gap-filling capability within a compressiveloading range that is safe for certain interface applications includingan IC die with an exposed face. Various soft thermal gap-fillermaterials can also be used within thermal interfaces; however thesematerials generally offer relatively low thermal conductivity, renderingthem unsuitable for high-output heat-producing electronic devices suchas a processor or GPU. Various phase-change thermal materials can offergap-filling with limited grease-pumping characteristics, however thephase-change properties of these materials can fail over time, inaddition to phase-change material leakage from the thermal interface.Liquid metal thermal materials can offer high thermal conductivitygap-filling, however such materials are relatively costly, can leak fromthermal interfaces, and can adversely react with other thermal interfacecomponents, causing catastrophic thermal interface and componentfailures.

The use of individual thermal interface materials, as described above,can lead to significant challenges in creating a stable, highperformance, reliable thermal interface that can make and maintaineffective thermal contact with both semiconductor device surfaces andcorresponding heat sink devices. Both semiconductor device surfaces andheat sinks can have non-planar interface surfaces, e.g., convex orconcave, which can create relatively large gaps that must be filled withthermally conductive material to ensure efficient electronic devicecooling. Many thermal interface materials are available which yieldacceptable thermal performance, e.g., 15-20 C-mm²/W, under high thermalload, however, none of these materials also offer adhesive properties.

According to embodiments, various beneficial combinations of two or morethermally conductive and adhesive materials can be used, in combination,to create a number of adhesive-bonded thermal interface embodiments.Such embodiments can enable an interface having low thermal resistancewithout the need for external mechanical latches and/or attachmenthardware, which can be useful on space-constrained printed circuit board(PCB) designs. In some embodiments, adhesive materials can be used incombination with various types of mechanical latches or attachmenthardware, to create a number of hybrid adhesive/mechanically bondedthermal interface embodiments. Such embodiments can be useful foreffectively managing area required for mechanical latches or attachmenthardware, while providing a thermally interface solution that can beeasily reworked.

Thermal interfaces according to embodiments can have enhanced stability,reliability and durability, relative to single-material thermalsolutions, over time and/or repeated thermal cycles. Such interfaces maynot manifest “grease pumping” behavior, can be durable within “shock andvibration” environments, and can be compliant and compressible under theapplication of a relatively low compression force. According toembodiments, such thermal interfaces can be used to fill a relativelywide range of surface irregularities and/or gaps between heat-producingelectronic device and heat sink surfaces, without being subject toadverse chemical interactions between various materials. Embodiments canprovide relatively low-cost, simple and straightforward thermalinterface implementation with minimal surface preparation requirements,processing, and material handling issues.

Certain embodiments relate to efficient transfer of heat from aheat-producing electronic device, through adhesive-bonded thermalinterface structures, to a heat sink. FIG. 1 depicts an apparatus usefulfor transferring heat from a heat-producing electronic device 114,through a thermally conductive material 112, e.g., a thermal grease,thermal paste, thermal gel or phase-change material, contained within aninner perimeter 124, to the heat sink 116, according to embodiments.Adhesive material 104 is used to hold the heat sink 116, thermallyconductive material 112, and heat-producing electronic device 114together as an assembly. In embodiments, the depicted apparatus can havelow thermal resistance, enhanced stability, reliability and durabilityover time and/or repeated thermal cycles. Embodiments of the apparatuscan be useful in cooling heat-producing electronic devices such asprocessor ICs, GPUs, multi-chip electronic modules and other electronicdevices requiring robust heat transfer/cooling. Such electronic devicescan be located within a wide variety of electronic equipment includingcomputing, server, laboratory, medical and telecommunications devicesand systems.

FIG. 1 includes two consistent views; side view 100 and cross-sectionA-A view 150. View 150 is a cross-section view of the cooling apparatus,the cooling apparatus being sectioned along line A-A of view 100,FIG. 1. As the two views 100 and 150 depict consistent features of theembodiments, the discussion of FIG. 1 herein is generally directedtowards the various features without reference to a particular view.Both views 100 and 150 depict the apparatus in an assembledconfiguration. Embodiments of the present disclosure can be used inconjunction with a wide variety of heat-producing electronic devices andmodules, including ICs.

A cooling apparatus designed according to embodiments can use adhesivematerials, e.g., thermal tape, to hold a heat sink onto a heat-producingelectronic device. Use of adhesive materials can enable implementationof thermal interfaces including high thermal conductivity, non-adhesivethermal pad material without the need for mechanical latches or loadretention hardware. Such thermal interfaces can be useful for conservingarea on space-constrained PCB designs.

Thermal measurements of test hardware constructed and operated accordingto embodiments have demonstrated and quantified significant efficiencyincrease of a thermal interface between a heat-producing electronicdevice and a heat sink. Measurements have shown significant reductionsin electronic device operating temperature, decreases in interfacethermal resistance and increases in heat sink operating temperatureresulting from improved thermal interface characteristics.

Various combinations of thermal and adhesive materials/materialconfigurations can be used in embodiments to implement a wide range ofadhesive-bonded thermal interfaces. According to embodiments,combinations of multiple thermally conductive materials can be arrangedin multiple layers within an adhesive perimeter to form a thermallyconductive interface between one or more IC(s) and a heat sink. Anarrangement of thermally conductive materials, in conjunction with theuse of adhesive material(s) can provide a thermally conductive interfacethat makes use of the beneficial properties, e.g., thermal conductivity,of each of the materials while managing or eliminating the manifestationof material properties/characteristics, e.g., grease pumping, which aredetrimental to the thermal interface.

Certain aspects of various embodiments such as the use of low-costmaterials and a relatively simple, low-cost assembly process can be usedto manage and/or limit the implementation cost of high-efficiencythermal interfaces. A cooling apparatus designed according to certainembodiments may be relatively simple to assemble and rework, which canallow straightforward field replacement electronic devices and heatsinks for complex systems such as water-cooled systems. Such simplicityof assembly and rework can be useful in effectively managing or reducingelectronic system field maintenance costs. Embodiments of the presentdisclosure can be used to provide cost-effective cooling apparatuses foruse with heat producing electronic devices, by using existing and provenheat sink, thermally conductive material, TIM and electronic devicetechnologies and materials. A cooling apparatus designed according toembodiments may be compatible with existing and proven electronicdevices, PCBs and electronic systems and may be a useful andcost-effective way to provide efficient cooling for heat-producingelectronic devices. A cooling apparatus constructed according toembodiments of the present disclosure may be installed on an existingheat-producing electronic device within an existing electronic system.

FIG. 1 depicts a cooling apparatus that does not require mechanicalfasteners to hold the heat sink 116 onto the heat-producing electronicdevice 114. Such an apparatus can be useful in PCB designs havinglimited space available for cooling devices such as heat sinks.Embodiments of the present disclosure can be useful in providingefficient and cost-effective cooling apparatuses for use withheat-producing electronic devices 114 by using existing and proven heatsink, thermally conductive material, TIM and electronic devicetechnologies. According to embodiments, heat-producing electronic device114 can include one or more ICs. Such IC(s) can be fabricated in a widevariety of IC design styles and technologies including, but not limitedto, complementary metal-oxide semiconductor (CMOS), silicon on insulator(SOI), analog and hybrid technologies. In embodiments, a heat-producingelectronic device 114 can also include other types of electronicmodule(s) or semiconductor device(s). Although FIG. 1 depicts aheat-producing electronic device 114 having a lid 102, according toembodiments, heat-producing electronic devices can include bothconventional lidded or lidless package styles.

The electronic device surface 108 can include backside surface(s) of oneor more ICs, or the lid 102 that is in thermally conductive contact withone or more heat-producing circuits, e.g., ICs, of the heat-producingelectronic device 114. In some embodiments, electronic device surface108 may be substantially planar, as depicted in FIG. 1. In someembodiments, however, electronic device surface 108 can be warped orbowed, and can have roughnesses or surface irregularities such as pitsor bumps. Warp or bow of electronic device surface 108 of certainpackaged devices can result from a coefficient of thermal expansion(CTE) difference between at least one electronic device and a package orsubstrate upon which the device is mounted. As an example, in someapplications, an electronic device surface 108 may have flatnessvariations in a range between 75 μm to 250 μm across the surface 108.

A heat sink 116 can be useful for efficiently transferring anddissipating heat from a heat-producing electronic device 114, in orderto ensure that the device 114 can function within a specified operatingtemperature range. A heat sink 116 can be designed to be cooled by air,refrigerant, water or other cooling fluids, and may involve the use ofmaterial phase changes, e.g., heat-pipe devices or technology. A heatsink can include heat-dissipating features such as fins, fluidcirculation channels or other thermally conductive attachment featuresused to dissipate heat from heat-producing electronic device 114.According to embodiments, the term “heat sink” can also be used inreference to devices also referred to as “heat spreaders.” Inembodiments, a heat sink 116 can be fabricated from various materialsthat are highly thermally conductive including, but not limited to,aluminum, copper and various alloys such as boron nitride (BN). In someembodiments, the heat sink surface 110 may be substantially planar, asdepicted in FIG. 1. In some embodiments, however, heat sink surface 110can be warped or bowed, and/or can have roughness or surfaceirregularities such as pits or bumps. For example, in some embodiments,an electronic device surface 108 may have flatness variations in therange between 25 μm and 100 μm, across the heat sink surface 110.

In some embodiments, heat sink 116 can include a protrusion 106 thatextends outward from the heat sink surface 110. The protrusion 106 canbe formed as a part of heatsink surface 110 through various materialforming processes, for example, casting or milling. The protrusion 106can be useful in creating, on the heat sink surface 110, an area definedby inner perimeter 124 for the placement and containment of a thermallyconductive material 112. In embodiments, protrusion 106 is locatedwithin outer perimeter 122 formed by adhesive material 104. According toembodiments, the height of protrusion 106, i.e., the distance it extendsaway from the heat sink surface 110, can be designed to be less thanadhesive material 104 thickness “T” and the thickness of thermallyconductive material 112. In embodiments, the thickness “T” also equalsthe distance, in an assembled configuration, between electronic devicesurface 108 and heat sink surface 110. Such a protrusion 106 height canensure that protrusion 106 does not contact electronic device surface108 when the heat sink 116 is assembled to the heat-producing electronicdevice 114. Avoiding contact of protrusion 106 with electronic devicesurface 108 can be useful in preventing damage, during assembly of theheat-electronic device 114 to the heat sink 116, and/or during asubsequent curing process that causes shrinkage of adhesive material104. In some embodiments, electronic device surface 108 can be thebackside of one or more IC die, which may be cracked or damaged ifpressed upon by protrusion 106. In some embodiments, the height of theprotrusion 106 can be in a range between 40% and 90% of adhesivematerial 104 thickness “T.” For example, if compressed thickness “T” ofthe adhesive material is 1.0 mm, then the protrusion height can be in arange between 0.4 mm and 0.9 mm. According to embodiments, a protrusion106 height in this range can be useful for containing, through surfacetension, thermally conductive material 112 within the inner perimeter124 and adjacent to the heat producing electronic device 114.

The boundaries formed by protrusion 106, heatsink surface 110 andelectronic device surface 108, in an assembled configuration, define aninner cavity that can be useful for containing thermally conductivematerial 112. Containment of thermally conductive material 112, e.g., athermal grease, can be useful in keeping the thermally conductivematerial 112 in contact with both electronic device surface 108 and heatsink surface 110, which can maintain an efficient thermal interfacebetween the heat-producing electronic device 114 and the heat sink 116.Protrusion 106 can be designed to optimally and efficiently position thethermally conductive material 112 so as to maintain contact withparticular high heat-dissipation area(s) of electronic device 114. Thiscontact can ensure efficient heat transfer from particularly highheat-dissipation electronic devices such as processors or GPUs.

Physical contact between certain types of thermally conductive materials112 and adhesive materials 104 can result in chemical interactions whichcan degrade desirable properties of one or both materials. Such propertydegradation can result in eventual catastrophic thermal interfacefailures. For example the bonding properties of adhesive material 104can be compromised through contact with particular types of thermallyconductive materials 112, which can result in a decrease in the bondstrength of adhesive material 104. A decrease in the bond strength ofadhesive material 104 can result in the adhesive material 104 failing tohold the heat-producing electronic device 114 to the heat sink 116,and/or allowing leakage of thermally conductive material 112 from theinner cavity. Protrusion 106 can be useful in providing a physicalbarrier to separate thermally conductive material 112 from adhesivematerial 104, and thus prevent the results of undesirable chemicalinteractions, such as a decrease in adhesive material 104 bond strength.

In embodiments where a heat-producing electronic device 114 is disposedin a vertical orientation, as depicted in view 100, containment of thethermally conductive material 112 within the inner cavity bounded byprotrusion 106 can be particularly useful. Containment by protrusion 106can prevent the thermally conductive material 112 from pooling, whenheated, at the bottom of the outer perimeter 122. Such pooling cancreate voids over high heat dissipation areas of electronic devicesurface 108, which can dramatically reduce the efficiency andeffectiveness of the thermal interface. Protrusion 106 can also beuseful in ensuring the integrity and stability of the thermal interfaceover repeated thermal cycles by mitigating “grease-pumping” or migrationof formable thermally conductive material 112.

According to embodiments, adhesive material 104 is located between theheat-producing electronic device 114 and heat sink 116 and is affixed toboth the heat sink surface 110 and to electronic device surface 108, asdepicted in view 100, FIG. 1. Adhesive material 104 can be placed orformed in a “ring” configuration that encloses protrusion 106 andthermally conductive material 112 as depicted in view 150, FIG. 1. Outerperimeter 122 corresponds to an interior edge of adhesive material 104that encloses protrusion 106. Adhesive material exterior perimeter 126corresponds to the exterior edge of adhesive material 104. Theboundaries formed by the outer perimeter 122 of adhesive material 104,heatsink surface 110 and electronic device surface 108, in an assembledconfiguration, define an outer cavity that can be useful for enclosingprotrusion 106 and thermally conductive material 112.

According to embodiments, adhesive material 104 can be used in place ofmechanical fasteners including, but not limited to, latches, clips,screws and clamps, to hold together the assembly of heat sink 116,heat-producing electronic device 114 and thermally conductive material112. Adhesive material 104 is useful for holding the heat sink surface110 in an adjacent, coplanar orientation to the electronic devicesurface 108 of the heat-producing electronic device 114. Adhesivematerial 104 can be useful for creating a perimeter, i.e., outerperimeter 122, having a thickness “T” above the surface it is appliedto, e.g., heat sink surface 110. In some embodiments, outer perimeter122 can be used to contain a formable thermally conductive material 112.Containment of thermally conductive material 112 can be useful inpreventing it from flowing, when heated, away from high heat-producingregions of electronic device surface 108 and from heat sink surface 110.Outer perimeter 122 can also be useful in preventing “grease pumping” ormigration of thermally conductive material 112.

According to embodiments, the adhesive material 104 can be apressure-sensitive adhesive (PSA) having relatively robust bondingproperties. PSAs can include, but are not limited to, double-sidedadhesive tapes, adhesive material sheets, adhesive liquids, gels,curable gels, and adhesives in aerosol formulations. In someembodiments, adhesive material 104 can include thermally conductivematerials such as aluminum mesh. In some embodiments, adhesive material104 can be thermally non-conductive, and in some embodiments adhesivematerial 104 can be thermally conductive and configured transfer heatbetween the electronic device surface 108 and the heat sink surface 110.For example, the thermal impedance of a double-sided thermallyconductive tape can be approximately 1.0° C.-in²/W. According toembodiments, a thermally conductive adhesive material 104 can be used asa supplemental heat-transfer element, in conjunction with a formablethermally conductive material 112 and/or with a TIM. Adhesives used inembodiments generally do not include curable thermal greases orphase-change materials such as solder. In some embodiments, adhesivematerial 104 can be chemically inert, i.e., non-reactive, with respectto the formable thermally conductive material 112. A chemically inertadhesive material 104 can be useful in preventing undesirable chemicalreactions with thermally conductive material 112, which can prevent thedegradation of desirable properties of either material. In embodiments,adhesive material 104 can have a thickness between 0.05 mm and 1.0 mm,depending on a particular application. For example, an aerosol adhesivecan be at thin as 0.05 mm and a double-sided thermally conductive tapecan have a thickness in a range, for example, between 0.2 mm and 0.3 mm.The adhesion strength of commercially available adhesives can be in arange, for example, between 10 psi and 30 psi.

According to embodiments, a PSA can be applied through various processincluding, but not limited to, printing, stenciling, dispensing, e.g.,through a syringe or nozzle, or through an aerosol spray, onto at leastone of the electronic device surface 108 and the heat sink surface 110.In some embodiments, adhesive material 104 can be a PSA that requiresapplication of a specified pressure for a specified time duration inorder for adhesive activation to occur. Certain PSAs can require anapplication pressure in a range between 5 psi and 20 psi, for severalseconds in order to properly activate adhesion. For example, to affixcertain double-sided adhesive tapes, an application pressure of 10 psifor 20 seconds is required to its activate adhesion. According toembodiments, application pressure and time may be precisely timed and/ormeasured in order to ensure to ensure proper PSA activation.

In some applications, during the operating life of the heat-producingelectronic device 114, a heatsink, e.g., 116, adhesive material 104and/or thermally conductive material 112 may need to be replaced orreattached to a heat-producing electronic device 114, through a reworkprocess. According to embodiments, certain types of adhesive material104 can be removable, which can allow parts of the assembly includingheat sink 116 and heat-producing electronic device 114 to be reworked,repaired or replaced. By way of example, a double-sided thermal adhesivetape can require a force in a range between 60 psi and 100 psi toremove. Such a range of removal forces can depend on the temperature ofthe adhesive; in some applications, elevating the temperature of anadhesive material 104 may reduce the removal force, and facilitate theadhesive's removal.

In some embodiments, an outline of the adhesive material 104 can defineat least one vent 120, i.e., opening, formed between the inner perimeter124 and adhesive material exterior perimeter 126. Vent 120 can be usefulfor equalizing pressures internal to and external to adhesive material104. Such pressures can be created during thermal excursion cycles orpossibly from outgas sing of thermally conductive material 112. Pressureequalization through vent 120 can prevent catastrophic thermal interfacefailure by minimizing pressure changes within the outer cavity.Minimizing pressure changes can be useful in preventing the detachmentor dislodging of the adhesive material 104 from the heat sink surface110 and/or electronic device surface 108. In embodiments where theheat-producing electronic device 114 is mounted vertically, Vent 120 canbe located on a top or upper surface of adhesive material 104.

In some embodiments, affixing of the heat sink 116 to the heat-producingelectronic device 114 can include an adhesive material curing process.Curing the adhesive material 104 can be useful in setting or “fixing”the adhesive, which can enhance and strengthen the bond between theheat-reducing electronic device 114 and the heat sink 116. An adhesivematerial curing process can also cause shrinkage or contraction of theadhesive material 104. A curing process can include maintaining anadhesive at specified temperature for a specified amount of time. Thespecified temperature and time may be dependent on factors such as theadhesive type/formulation and physical dimensions of the adhesive. Forexample, in some embodiments a particular adhesive may be cured at atemperature of 70° C. for 24 hours, followed by curing at a temperatureof 22° C. for 7 days. Adhesive types can also include two-part “blended”adhesives which may not require a curing process, or which may cure atroom temperature.

Certain types of adhesive material 104 can shrink during curing process,which can provide a tensile force “F” between the heat sink surface 110and the electronic device surface 108 in addition to a tensile forceprovided the adhesive prior to a curing process. Tensile force “F” canserve to pull the heat producing electronic device 114 and the heat sink116 towards each other, which can result in compression of thermallyconductive material 112 that reduces the thermally conductive material112 thickness “T,” or “bond line” thickness. Reduction of the thickness“T” can shorten the heat conduction path length through the thermallyconductive material 112. Shortening the conduction path length can lowerthe thermal resistance of the thermally conductive material 112 as wellas the entire thermal interface. Lowering thermal resistances can resultin increased efficiency and effectiveness of thermal interface betweenthermally conductive material 112 and the electronic device surface 108and heat sink surface 110. In embodiments, the time and temperature of acuring process can be precisely controlled so that the protrusion 106does not contact or press on the electronic device surface 108 during orafter the curing process. The shrinking or compression of adhesivematerial 104 can also be used to effectively reduce the protrusion 106height necessary to contain the thermally conductive material 112 withinthe inner cavity.

Thermally conductive material 112 can be useful in cooling theheat-producing electronic device 114 by providing an efficient thermalinterface path having low thermal resistance between electronic devicesurface 108 and heat sink surface 110. Such a thermal interface path canbe suitable for removing large amounts of heat from a heat-producingelectronic device 114, for example a high power output processor or GPU.According to embodiments, thermally conductive material 112 can be a“formable” material, i.e., one that generally responds to compressiveforces by assuming the shape of a cavity or structure containing it. ATIM pad, in contrast to a “formable” material, may have a certain degreeof resiliency, however, will not generally assume the shape of a cavityor structure containing it in response to compressive forces applied toit. Thermally conductive material 112 can be useful in filling in heatsink surface 110 and electronic device surface 108 roughnesses, reducingair gaps, and providing increased surface area for heat transfer andmore efficient electronic device cooling. According to embodiments,thermally conductive material 112 can be a formable, highly thermallyconductive compound having relatively low thermal resistance. Forexample, such compounds may have thermal resistance in a range between0.032° C.-cm²/W and 0.162° C.-cm²/W. In embodiments, thermallyconductive materials 112 can be resilient or non-resilient. Thermallyconductive materials 112 can include, but are not limited to, thermalgreases, pastes, gels, curable gels and binders with metal particulates.In embodiments, thermally conductive material 112 can be applied, toheat sink surface 110 or electronic device surface 108, by dispensing orstenciling to a thickness of up to 1.0 mm. In embodiments, use of athermally conductive material 112 and adhesive material 104 which arechemically inert with respect to one another can be useful in preventingthe degradation of useful properties of either material.

In embodiments, the inner cavity is filled with a precisely measured anddispensed volume of thermally conductive material 112 sufficient to fillthe inner cavity. If an amount of thermally conductive material 112placed in the inner cavity is insufficient to fill the inner cavity,significant portions of the heat sink surface 110 and/or electronicdevice surface 108 may not be in thermally conductive contact with thethermally conductive material 112. Such lack of contact can diminishoverall thermal conductivity and cooling capacity of the thermalinterface. If an amount of thermally conductive material 112 placed inthe inner cavity is in excess of the capacity of the inner cavity, theexcess thermally conductive material 112 may flow outwards from thecavity and break the surface tension, which can cause a pool ofthermally conductive material 112 to form despite the protrusion 106.Such pooling can also diminish overall thermal conductivity and coolingcapacity of the thermal interface.

Pressing the heat sink 116 and the heat-producing electronic device 114together with a compressive force can be useful in spreading out theformable thermally conductive material 112 to fill in the inner cavitycontaining it. Such compression can also be useful in flattening and/orthinning the thermally conductive material 112 bond line. Flattening thebond line can create an efficient thermal interface between theheat-producing electronic device 114 and the heat sink 116, and canimprove heat sink and electronic device surface thermal interfacecharacteristics.

FIG. 2 depicts an apparatus useful for transferring heat from aheat-producing electronic device 114, through a thermally conductive TIMpad 212 contained within an inner perimeter 222 of adhesive material104, to the heat sink 116, according to embodiments consistent with thefigures. Adhesive material 104 is used to hold the heat sink 116, TIMpad 212, and heat-producing electronic device 114 together as anassembly. In embodiments, the depicted apparatus can have low thermalresistance, and can be useful in cooling heat-producing electronicdevices such as processor ICs, GPUs and multi-chip electronic modules.

FIG. 2 includes two consistent views; side view 200 and cross-sectionB-B view 250. View 250 is a cross-section view of the cooling apparatus,the cooling apparatus being sectioned along line B-B of view 200, FIG.2. As the two views 200 and 250 depict consistent features of theembodiments, the discussion of FIG. 2 herein is generally directedtowards the various features without reference to a particular view.Both views 200 and 250 depict the apparatus in an assembledconfiguration.

FIG. 2 depicts a cooling apparatus that does not require mechanicalfasteners to hold the heat sink 116 onto the heat-producing electronicdevice 114. Such an apparatus can be useful in PCB designs havinglimited space available for cooling devices such as heat sinks.According to embodiments, adhesive material 104 can be used in place ofmechanical fasteners including, but not limited to, latches, clips,screws and clamps, to hold together the assembly of heat sink 116,heat-producing electronic device 114 and TIM pad 212. In embodiments,adhesive material 104 is located between the heat-producing electronicdevice 114 and heat sink 116 and is affixed to both the heat sinksurface 110 and to electronic device surface 108, as depicted in view200, FIG. 2. Adhesive material 104 can be placed or formed in a “ring”having a perimeter 222 corresponding to an interior edge of adhesivematerial 104.

In embodiments, TIM pad 212 is located within perimeter 222, as depictedin view 250, FIG. 2. In an assembled configuration, the boundariesformed by the perimeter 222 of adhesive material 104, heatsink surface110 and electronic device surface 108 define a cavity that can be usefulfor containing TIM pad 212. Adhesive material 104 has a thickness “T”above the surface it is applied to, e.g., heat sink surface 110.Containment of a TIM pad 212, e.g., a carbon fiber pad, can be useful inkeeping at least a portion of one surface of the TIM pad 212 inthermally conductive contact with electronic device surface 108, and atleast a portion of the opposing surface of the TIM pad 212 in thermallyconductive contact with heat sink surface 110. Such thermally conductivecontact allows TIM pad 212 to cool the heat-producing electronic device114 by providing an efficient, thermally conductive path having lowthermal resistance between the electronic device surface 108 and theheat sink surface 110. In some embodiments, an adhesive material 104that is thermally conductive can be used as a supplemental heat-transferelement in conjunction with a TIM pad 212. Particular highheat-dissipation area(s) of electronic device surface 108 can correspondto certain electronic devices having relatively high heat dissipation,such as a processors or GPUs. In embodiments, adhesive material 104 canbe useful in optimally and efficiently positioning the TIM pad 212 sothat it remains in a fixed position and maintains thermally conductivecontact with these high heat-dissipation area(s), which can result inefficient heat transfer.

Adhesive material 104 can be chemically inert, i.e., non-reactive, withrespect to TIM pad 212. A chemically inert adhesive material 104 can beuseful in preventing undesirable chemical reactions with the TIM pad212, which can prevent the degradation of useful properties of eithermaterial. In some applications, during the operating life of theheat-producing electronic device 114, a heatsink, e.g., 116, adhesivematerial 104 and/or TIM pad 212 may need to be replaced or reattached toa heat-producing electronic device 114, through a rework process.According to embodiments, certain types of adhesive material 104 can beremovable, which can allow the assembly including heat sink 116 andheat-producing electronic device 114 to be reworked, repaired orreplaced.

Certain types of adhesive material 104 can shrink during curing process,which can provide a tensile force “F” between the heat sink surface 110and the electronic device surface 108 in addition to a tensile forceprovided the adhesive prior to a curing process. Tensile force “F” canserve to pull the heat producing electronic device 114 and the heat sink116 towards each other, which can result in compression of TIM pad 212that reduces the TIM pad 212 thickness. Reduction of the thickness “T”of TIM pad 212 can shorten the heat conduction path length through theTIM pad 212, which can lower the thermal resistance of the TIM pad 212and the thermal resistance of the entire thermal interface. Loweringthermal resistances can result in increased efficiency and effectivenessof thermal interface between TIM pad 212 and the electronic devicesurface 108 and heat sink surface 110.

In contrast to a “formable” thermally conductive material, a TIM pad 212may have a particular degree of resiliency, however a TIM pad 212 willnot generally, in response to applied compressive forces, assume theshape of a cavity or structure containing it. A TIM pad 212 maintainingits overall shape can be useful in maintaining contact, over time andmultiple thermal/flexing cycles, between the TIM pad 212 and the heatsink surface 110 and the electronic device surface 108. Unlike aformable thermally conductive material, a TIM pad is a solid-statematerial, not subject to reflow, “grease pumping” or shape changingbehaviors when heated. According to embodiments, TIM pad 212 can be ahighly thermally conductive element having relatively low thermalresistance. For example, such TIMs may have thermal resistance in arange between 0.010° C.-cm²/W and 0.100° C.-cm²/W. Certain TIM pads canhave a low thermal resistance relative to a thermally conductivematerial 112, FIG. 1. According to embodiments, TIM pad 212 can beresilient or non-resilient, and is generally a pre-formed, thermallyconductive element that is not an intrinsic part of an electronic deviceand/or electronic device package. It can be understood that a TIM pad212 is not an adhesive and does not exhibit adhesive properties orforces. In some embodiments a compliant, compressible and resilient TIMpad 212 can be useful in providing enhanced surface thermal interfaceswith heat sink surface 110 and electronic device surface 108 by at leastpartially filling in roughnesses and reducing air gaps between thesurfaces. Enhanced surface thermal interfaces can enable efficient heattransfer and electronic device cooling by creating a low thermalresistance path between heat-producing electronic device 114 and heatsink 116.

TIM pad 212 can be fabricated from materials including, but are notlimited to, carbon fibers, metal, phase-change materials, compressiblesolid graphite and composite materials. A soft metal alloy thermalinterface material (SMA-TIM) can include a compressible and malleablemetal such as indium, which can provide uniform thermal resistance atrelatively low applied stress in a compressed interface. For example, apressure range between 35 psi and 100 psi can yield relatively lowthermal resistances compared to formable thermally conductive materialssuch as thermal greases, pastes or gels. For example, a 0.05-0.3 mmthick SMA-TIM can have a thermal conductivity of 0.04° C.-cm²/W at anapplied pressure of 60 psi. TIM pads can have a limited gap fillingrange, for example, certain TIM pads can provide 150 μm (6 mils) of gapfilling compliance.

Certain types of pre-formed TIM pads 212, e.g., graphite pads, can berelatively fragile and subject to damage during handling and/or assemblyprocess(s). For example, if a TIM pad 212 falls out of the cavity formedbetween a heat-producing electronic device and a heat sink, it may bedamaged. In embodiments, a tacking adhesive material 218 can beparticularly useful in preventing possible damage to the TIM pad 212 byholding or tacking a TIM pad 212 in an aligned position adjacent to theheat sink surface 110 or electronic device surface 108 within the cavityduring an assembly process. In embodiments, small amounts of a tackingadhesive material 218 can be applied to a surface of the TIM, the heatsink surface 110 or electronic device surface 108 prior to placement ofthe TIM pad 212 within the cavity. For example, a dot of tackingadhesive material 218 can be applied to the center of an area forreceiving a TIM pad on the heat sink surface 110 or electronic devicesurface 108. Upon contact with the opposing heat sink surface 110 andelectronic device surface 108, or upon compression of the thermalinterface assembly, tacking adhesive material 218 can spread out into athin layer across at least a portion of the opposing surface(s). Tackingadhesive material 218 can have a relatively low tendency to reflow whenheated, and in embodiments may not cover the entire area close byperimeter 222. According to embodiments, tacking adhesive material 218can include various material types such as transient evaporativematerials, e.g., isopropyl alcohol, or thermally conductive materialsand/or adhesives such as thermal greases, pastes or gels. Tackingadhesive material 218 can be useful in providing a thin, “tacky,” i.e.,temporary, adhesive layer useful for holding the TIM pad 212 in placefor the duration of the assembly process.

FIG. 3 depicts an apparatus useful for transferring heat from aheat-producing electronic device 314, through a TIM pad 312 andthermally conductive material 326 contained within a perimeter 322 ofadhesive material 104, to heat sink 116, according to embodimentsconsistent with the figures. Adhesive material 104 is used to hold theheat sink 116, TIM pad 312, thermally conductive material 326 andheat-producing electronic device 314 together as an assembly. Inembodiments, the depicted apparatus can have low thermal resistance, andcan be useful in cooling heat-producing electronic devices such asprocessor ICs, GPUs and multi-chip electronic modules.

FIG. 3 includes two consistent views; side view 300 and cross-sectionC-C view 350. View 350 is a cross-section view of the cooling apparatus,the cooling apparatus being sectioned along line C-C of view 300, FIG.3. As the two views 300 and 350 depict consistent features of theembodiments, the discussion of FIG. 3 herein is generally directedtowards the various features without reference to a particular view.View 300 depicts the apparatus in an assembled configuration, while view350 depicts the apparatus prior to assembly.

FIG. 3 depicts a cooling apparatus that does not require mechanicalfasteners to hold the heat sink 116 onto the heat-producing electronicdevice 314. Such an apparatus can be useful in PCB designs havinglimited space available for cooling devices such as heat sinks.According to embodiments, adhesive material 104 can be used in place ofmechanical fasteners including, but not limited to, latches, clips,screws and clamps, to hold together the assembly of heat sink 116,heat-producing electronic device 314, thermally conductive material 326and TIM pad 312. Thermally conductive material 326 can be understood tobe consistent, particularly in respect to thermal and mechanicalproperties, with thermally conductive material 112, FIG. 1. Similarly,TIM pad 312 can be understood to be consistent with TIM pad 212, FIG. 2.Thermally conductive material 326 can be chemically inert, i.e.,non-reactive, with respect to TIM pad 312 and adhesive material 104. Achemically inert adhesive material 104 can be useful in preventingundesirable chemical reactions with the TIM pad 312, which can preventthe degradation of useful properties of either material. In embodiments,adhesive material 104 is located between the heat-producing electronicdevice 314 and heat sink 116 and is affixed to both the heat sinksurface 110 and to electronic device surface 308, as depicted in view300, FIG. 3.

Although a lid, e.g., 102, FIG. 1, is not depicted as part ofheat-producing electronic device 314 in FIG. 3, in some embodiments,heat-producing electronic device 314 can include a lid. Adhesivematerial 104 can be placed or formed in a “ring” having a maximumthickness “T” above the surface it is applied to, e.g., heat sinksurface 110 and a perimeter 322 corresponding to an interior edge ofadhesive material 104.

In embodiments, TIM pad 312 and thermally conductive material 329 arelocated within perimeter 322, as depicted in view 350, FIG. 3. In anassembled configuration, the boundaries formed by the perimeter 322 ofadhesive material 104, heatsink surface 110 and electronic devicesurface 308 define a cavity that can be useful for containing thermallyconductive material 326 and TIM pad 312. Containment of a TIM pad 312,e.g., a carbon fiber pad, can be useful in keeping at least a portion ofone surface of the TIM pad 312 in thermally conductive contact withelectronic device surface 308, and at least a portion of the opposingsurface of the TIM pad 312 in thermally conductive contact with heatsink surface 110. Such thermally conductive contact allows TIM pad 312in conjunction with thermally conductive material 326 to cool theheat-producing electronic device 314 by providing an efficient,thermally conductive path having low thermal resistance between theelectronic device surface 308 and the heat sink surface 110. Particularhigh heat-dissipation area(s) of electronic device surface 308 cancorrespond to certain electronic devices having relatively high heatdissipation, such as a processors or GPUs. In some embodiments, theseareas can correspond to contact region 330, view 300. In embodiments,thermally conductive material 326 and adhesive material 104 can beuseful in optimally and efficiently positioning the TIM pad 312 so thatit remains in a fixed position and maintains thermally conductivecontact with these high heat-dissipation area(s), which can result inefficient heat transfer. In some embodiments, an adhesive material 104that is thermally conductive can be used as a supplemental heat-transferelement in conjunction with a TIM pad 312.

According to embodiments, both the electronic device surface 308 and theheat sink surface 110 can independently deviate from a completely planarsurface profile. Each of the surfaces 110 and 308 can include anycombination of convex, concave, warped, bowed, rippled, rough, pittedand bumped surface characteristics. For example, electronic devicesurface 308 can have overall flatness deviations from a completelyplanar surface in a range between 75 μm and 250 μm across the surface308 of the electronic device. Similarly, a heat sink surface 110 canhave overall flatness deviations in a range between 25 μm and 100 μmacross surface 110 of the heat sink. View 300 depicts electronic devicesurface 308 as having a convex surface profile. Flatness deviation suchas warp or bow, in some embodiments, can result from a CTE differencebetween at least one electronic device and the substrate/package uponwhich the device is mounted. In this discussion, it is understood thatthe “electronic device” and the “substrate/package” referred to aboveare both elements of the heat-producing electronic device 314.

According to embodiments, the electronic device surface 308 can includebackside surface(s) of one or more ICs, or a lid 102 that is inthermally conductive contact with one or more heat-producing circuits,e.g., ICs, of the heat-producing electronic device 314. In embodimentswhere the heat-producing electronic device 314 includes a lid, e.g.,102, FIG. 1, such a lid can also assume a non-planar shape, e.g., convexor concave, in accordance with a corresponding non-planar shape of theheat-producing electronic device 314. The above-described deviationsfrom a completely planar surface profile can result in gaps, withinthermal interfaces between two mating, non-planar, surfaces, as depictedby gap regions 328, view 300. Such gaps can be relatively narrow andformed, for example, as a result of a protruding feature of a warped,convex heat-producing electronic device 314 coming into contact with amore planar heat sink surface 110. If such gaps remain unfilled withthermally conductive material, the thermal conductivity of a thermalinterface between the surfaces can be significantly degraded, relativeto thermal interfaces between more planar surfaces having a smaller gapsize.

In some embodiments a compliant, compressible and resilient TIM pad 312can be useful in enhancing thermal interfaces with heat sink surface 110and electronic device surface 308 by at least partially filling inroughnesses and reducing air gaps between the surfaces. The gap-fillingcapability of commercially available, solid-state TIM pads having highthermal conductivity, e.g., 312, is typically in a limited range between25 μm and approximately 125 μm-150 μm (≈6 mils) of compliance betweenadjacent thermally conductive surfaces. This thickness generallycorresponds to the contact region 330, view 300. This thickness rangecorresponds to a range of application pressures suitable for thermalinterfaces that directly contact the back of an IC die. The maximumdistance between two mated, thermally conductive surfaces can be, insome embodiments, in a range between 200 μm and 250 μm. Such distancescan leave gaps between a significant portion of the mating surfaces,e.g., gap regions 328, view 300, in cases where a TIM is the onlythermally conductive material positioned between the thermallyconductive surfaces.

In embodiments, thermally conductive material 326 can be applied, e.g.,dispensed or stenciled, onto an area of either the heat sink surface 110or the electronic device surface 308 corresponding to a perimeter of TIMpad 312, as depicted in view 350. As an example, certain thermallyconductive materials 326 can be stenciled to a thickness of up to 300 μmonto a surface. View 350 depicts thermally conductive material 326 priorto an assembly process. Thermally conductive material 326 can be appliedto either surface 110 or 308, for example, as rectangular shapes, dots,or a contiguous line that overlap(s) the outer edge of TIM pad 312, asdepicted in view 350. According to embodiments, the TIM pad 312 at leastpartially overlaps the formable thermally conductive material 326 whenthe heat-producing electronic device 314, TIM pad 312, thermallyconductive material 326 and heat sink 116 are assembled. In embodiments,compressive force applied during assembly process can cause thermallyconductive material 326 to fill gap regions 328, as depicted in view300. Filling gap regions 328 can be useful for enhancing the overallconductivity of a thermal interface by filling gaps having shapes orthicknesses which cannot be effectively filled by TIM pad 312. Such arelatively thin layer of thermally conductive material 326 can have alower tendency to reflow, when heated, than a thicker layer that mightbe used in thermal interfaces not including a TIM pad 312.

View 300 depicts thermally conductive material 326 pressed into andfilling gap regions 328 between TIM pad 312 and heat sink surface 110,however, in some embodiments, thermally conductive material 326 can beused to fill similar gap regions between TIM pad 312 and electronicdevice surface 308. In embodiments, thermally conductive material 326can be useful in preventing possible damage to the TIM pad 312 byholding or tacking a TIM pad 312 in an aligned position within thecavity, adjacent to the heat sink surface 110 or electronic devicesurface 308, for the duration of the assembly process. Such tacking canalso be useful to avoid the need for TIM alignment pins, which canincrease thermal interface cost and complexity, and can consume criticalhardware real estate on a PCB.

The use of two thermal interface materials each with unique, beneficialproperties, e.g., thermally conductive material 326 and TIM pad 312, ina stacked combination can provide a reliable, stable and efficientthermal interface between a heat-producing electronic device and a heatsink. Embodiments of the present disclosure can provide a combination ofrobust TIM compression and full “gap-filling” bond line coverage over anentire non-planar electronic device surface, e.g., 308. Such fullcoverage may not be possible using traditional thermal interfacetechniques. Embodiments can also provide enhanced thermal conductivity,compared to other thermal interface implementations, through the use ofa TIM pad in conjunction with a relatively thin layer of thermallyconductive material. According to embodiments, a high-performance,reliable thermal interface can be created to fill cumulative thermalinterface gaps that are greater than 300 μm. If the thermal conductivityof a TIM pad, e.g., 312, is greater than the conductivity of thermallyconductive material, e.g., 326, an assembly including a TIM padsupplemented with a relatively thin layer of thermally conductivematerial can provide higher overall thermal conductivity than anassembly including just a relatively thick layer of thermally conductivematerial.

In embodiments, the use of a highly compressible, dispensable thermallyconductive material at thermal interface perimeter locations can allowfull compressibility of the TIM, which can result in overall thermalinterface performance enhancement and reliability. A dispensable orstencil-printed thermal interface material, e.g., thermal grease, can beapplied over relatively low power dissipation regions, e.g., thosecorresponding to memory devices, of an electronic device surface. Theseregions can correspond to larger thermal interface gaps than gapsadjacent to higher power interface regions, e.g., those corresponding toa processor or GPU ICs. Thermally conducting gap-filling materials canbe useful at thermal interface peripheral locations and/or corners toprovide mechanical damping to enhance TIM interface integrity duringshock and vibration events that can occur during product handling orshipment.

Embodiments of the present disclosure can use the lateral heatconduction of a TIM pad in conjunction with the conduction ofoverlapping thermal interface material and TIM pad layers to assist inheat removal from electronic device surface areas adjacent to relativelythick thermal interface material layers. Embodiments can provideimprovements and thermal interface performance relative to thermalinterfaces that include only thermally conductive materials or only TIMpads. Some embodiments can useful in mitigating or eliminating, throughthe placement of a TIM pad in relatively thin, high-strain bond lineregions adjacent to high power electronic devices, the phenomena of“grease pumping” and thermal gel delamination.

In some applications, during the operating life of the heat-producingelectronic device 314, a heatsink, e.g., 116, adhesive material 104,thermally conductive material 326 and/or TIM pad 312 may need to bereplaced or reattached to a heat-producing electronic device 314,through a rework process. According to embodiments, certain types ofadhesive material 104 can be removable, which can allow the assemblyincluding heat sink 116 and heat-producing electronic device 314 to bereworked, repaired or replaced.

Certain types of adhesive material 104 can shrink during curing process,which can provide a tensile force “F” between the heat sink surface 110and the electronic device surface 308 in addition to a tensile forceprovided the adhesive prior to a curing process. Tensile force “F” canserve to pull the heat producing electronic device 314 and the heat sink116 towards each other, which can result in compression of TIM pad 312that reduces the TIM pad 312 thickness. The resulting compression canalso be useful in forcing thermally conductive material 326 into gapregions 328, view 300, from area(s) where thermally conductive material326 is initially dispensed, 328, view 350. Reduction of the thickness“T” of TIM pad 312 can shorten the heat conduction path length throughthe TIM pad 312, which can lower the thermal resistance of the TIM pad312 and the thermal resistance of the entire thermal interface. Theinsertion of thermally conductive material 326 into gap regions can alsobe useful for lowering the thermal resistance of the entire thermalinterface. Lowering thermal resistances can result in increasedefficiency and effectiveness of thermal interface between TIM pad 312and the electronic device surface 308 and heat sink surface 110.

FIG. 4 depicts an apparatus useful for transferring heat from aheat-producing electronic device 314, through a TIM pad 412 andthermally conductive adhesive 404, to the heat sink 116, according toembodiments consistent with the figures. In embodiments, TIM pad 412partially overlaps and is contained within thermally conductive adhesive404. Thermally conductive adhesive 404 is used to hold the heat sink116, TIM pad 412 and heat-producing electronic device 314 together as anassembly, as depicted. In embodiments, the depicted apparatus can havelow thermal resistance, and can be useful in cooling heat-producingelectronic devices such as processor ICs, GPUs and multi-chip electronicmodules.

FIG. 4 includes two consistent views; side view 400 and cross-sectionD-D view 450. View 450 is a cross-section view of the cooling apparatus,the cooling apparatus being sectioned along line D-D of view 400, FIG.4. As the two views 400 and 450 depict consistent features of theembodiments, the discussion of FIG. 4 herein is generally directedtowards the various features without reference to a particular view.View 400 depicts the apparatus in an assembled configuration, while view450 depicts the apparatus prior to assembly.

View 450 depicts the overlapping positioning of thermally conductiveadhesive 404 and the TIM pad 412, prior to an assembly process and theapplication of a compressive force. View 400 depicts the thermallyconductive adhesive 404 and the TIM pad 412 in an assembledconfiguration, following the application of a compressive force. View400 depicts the results of the thermally conductive adhesive 404 beingpressed into a gap between the TIM pad 412 and the heat sink 116.

FIG. 4 depicts a cooling apparatus that does not require mechanicalfasteners to hold the heat sink 116 onto the heat-producing electronicdevice 314. Such an apparatus can be useful in PCB designs havinglimited space available for cooling devices such as heat sinks.According to embodiments, thermally conductive adhesive 404 can be usedin place of mechanical fasteners including, but not limited to, latches,clips, screws and clamps, to hold together the assembly of heat sink116, heat-producing electronic device 314 and TIM pad 412. TIM pad 412can be understood to be consistent with TIM pad 212, FIG. 2. Thermallyconductive adhesive 404 can be understood to be in adhesive materialhaving thermally conductive properties. For example, certaincommercially available thermally conductive adhesives 404 can have athermal impedance of 0.1° C.-in2/W at a recommended bond line thicknessof 0.28 mm (280 μm).

Thermally conductive adhesive 404 can be chemically inert, i.e.,non-reactive, with respect to TIM pad 412. A chemically inert thermallyconductive adhesive 404 can be useful in preventing undesirable chemicalreactions with the TIM pad 412, which can prevent the degradation ofuseful properties of either material. In embodiments, thermallyconductive adhesive 404 is located between the heat-producing electronicdevice 314 and heat sink 116 and is affixed to both the heat sinksurface 110 and to electronic device surface 308, as depicted in view400, FIG. 4. Although a lid, e.g., 102, FIG. 1, is not depicted as partof heat-producing electronic device 314 in FIG. 4, in some embodiments,heat-producing electronic device 314 can include a lid. Thermallyconductive adhesive 404 can be placed or formed in a “ring” having amaximum thickness “T” above the surface it is applied to, e.g., heatsink surface 110, and a perimeter 422 corresponding to an interior edgeof thermally conductive adhesive 404.

In embodiments, the outline of TIM pad 412 at least partially overlapswith perimeter 422 of thermally conductive adhesive 404, as depicted inview 450, FIG. 4. In an assembled configuration, thermally conductiveadhesive 404, heatsink surface 110 and electronic device surface 308define a cavity that can be useful for containing and TIM pad 412.Containment of a TIM pad 412, e.g., a carbon fiber pad, can be useful inkeeping at least a portion of one surface of the TIM pad 412 inthermally conductive contact with electronic device surface 308, and atleast a portion of the opposing surface of the TIM pad 412 in thermallyconductive contact with heat sink surface 110.

Such thermally conductive contact allows TIM pad 412 in conjunction withthermally conductive adhesive 404 to cool the heat-producing electronicdevice 314 by providing an efficient, thermally conductive path havinglow thermal resistance between the electronic device surface 308 and theheat sink surface 110. Particular high heat-dissipation area(s) ofelectronic device surface 308 can correspond to certain electronicdevices having relatively high heat dissipation, such as a processors orGPUs. In some embodiments, these areas can correspond to contact region430, view 400. In embodiments, thermally conductive adhesive 404 can beuseful in optimally and efficiently positioning the TIM pad 412 so thatit remains in a fixed position and maintains thermally conductivecontact with these high heat-dissipation area(s), which can result inefficient heat transfer. In embodiments, a thermally conductive adhesive404 be used as a supplemental heat-transfer element in conjunction withTIM pad 412.

Deviations from a completely planar heat sink or heat-producingelectronic device surface profile can result in gaps, within thermalinterfaces between two mating, non-planar, surfaces, as depicted by gapregions 428, view 400. Such gaps can be relatively narrow and formed,for example, as a result of a protruding feature of a warped, convexheat-producing electronic device coming into contact with a more planarheat sink surface. If such gaps remain unfilled with thermallyconductive material, the thermal conductivity of a thermal interfacebetween the surfaces can be significantly degraded, relative to thermalinterfaces between more planar surfaces having a smaller gap size. Insome embodiments a compliant, compressible and resilient TIM pad 412 canbe useful in enhancing thermal interfaces with heat sink surface 110 andelectronic device surface 308 by at least partially filling inroughnesses and reducing air gaps between the surfaces. The gap-fillingcapability of commercially available, solid-state TIM pads having highthermal conductivity, e.g., 412, is typically in a limited range between25 μm and approximately 125-150 μm (≈6 mils) of compliance betweenadjacent thermally conductive surfaces. This thickness generallycorresponds to the contact region 430, view 400. This thickness rangecorresponds to a range of application pressures suitable for thermalinterfaces that directly contact the back of an IC die. The maximumdistance between two mated, thermally conductive surfaces can be, insome embodiments, in a range between 200 μm and 250 μm. Such distancescan leave gaps between a significant portion of the mating surfaces,e.g., gap regions 428, view 400, in cases where a TIM is the onlythermally conductive material positioned between the thermallyconductive surfaces.

In embodiments, thermally conductive adhesive 404 can be applied, e.g.,dispensed or stenciled, onto an area of either the heat sink surface 110or the electronic device surface 308 that overlaps a perimeter of TIMpad 412, as depicted in view 450. As an example, certain thermallyconductive adhesives 404 can be stenciled to a thickness of up to 300 μmonto a surface. View 450 depicts thermally conductive adhesive 404 priorto an assembly process. Thermally conductive adhesive 404 can be appliedto either surface 110 or 308, for example, as one or more rectangularshapes, dots, or a contiguous line that overlap(s) the outer edge of TIMpad 412, as depicted in view 450. According to embodiments, the TIM pad412 at least partially overlaps the formable thermally conductiveadhesive 404 when the heat-producing electronic device 314, TIM pad 412and heat sink 116 are assembled. In embodiments, compressive forceapplied to the assembly can cause thermally conductive adhesive 404 tofill gap regions 428, as depicted in view 400. Filling gap regions 428can be useful for enhancing the overall conductivity of a thermalinterface by filling gaps having shapes or thicknesses which cannot beeffectively filled by TIM pad 412. Such a relatively thin layer ofthermally conductive adhesive 404 can have a lower tendency to reflow,when heated, than a thicker layer that might be used in thermalinterfaces not including a TIM pad 412. View 400 depicts thermallyconductive adhesive 404 pressed into and filling gap regions 428 betweenTIM pad 412 and heat sink surface 110, however, in some embodiments,thermally conductive adhesive 404 can be used to fill similar gapregions between TIM pad 412 and electronic device surface 308.

In embodiments, thermally conductive adhesive 404 can be useful inpreventing possible damage to the TIM pad 412 by holding or tacking aTIM pad 412 in an aligned position adjacent to the heat sink surface 110or electronic device surface 308, for the duration of the assemblyprocess. Such tacking can also be useful in avoiding the need for TIMalignment pins, which can increase thermal interface cost andcomplexity, and can consume critical hardware real estate on a PCB.

The use of two thermal interface materials each with unique, beneficialproperties, e.g., thermally conductive adhesive 404 and TIM pad 412, ina stacked combination can provide a reliable, stable and efficientthermal interface between a heat-producing electronic device and a heatsink. Embodiments can also provide enhanced thermal conductivity,compared to other thermal interface implementations, through the use ofa TIM pad in conjunction with a relatively thin layer of thermallyconductive adhesive. Thermally conducting gap-filling adhesive materialscan be useful at thermal interface peripheral locations and/or cornersto provide mechanical damping to enhance TIM interface integrity duringshock and vibration events that can occur during product handling orshipment.

In some applications, during the operating life of the heat-producingelectronic device 314, a heatsink, e.g., 116, thermally conductiveadhesive 404 and/or TIM pad 412 may need to be replaced or reattached toa heat-producing electronic device 314, through a rework process.According to embodiments, certain types of thermally conductive adhesive404 can be removable, which can allow the assembly including heat sink116 and heat-producing electronic device 314 to be reworked, repaired orreplaced.

Certain types of thermally conductive adhesive 404 can shrink duringcuring process, which can provide a tensile force “F” between the heatsink surface 110 and the electronic device surface 308 in addition to atensile force provided the adhesive prior to a curing process. Tensileforce “F” can serve to pull the heat producing electronic device 314 andthe heat sink 116 towards each other, which can result in compression ofTIM pad 412 that reduces the TIM pad 412 thickness. The resultingcompression can also be useful in forcing thermally conductive adhesive404 into gap regions 428, view 400, from area(s) where thermallyconductive adhesive 404 is initially dispensed, as depicted in view 450.Reduction of the thickness of TIM pad 412 can shorten the heatconduction path length through the TIM pad 412, which can lower thethermal resistance of the TIM pad 412 and the thermal resistance of theentire thermal interface. The insertion of thermally conductive adhesive404 into gap regions can also be useful for lowering the thermalresistance of the entire thermal interface. Lowering thermal resistancescan result in increased efficiency and effectiveness of thermalinterface between TIM pad 412 and the electronic device surface 308 andheat sink surface 110. In some embodiments, for example, the overallthermal resistance of a hybrid TIM and thermally conductive adhesivematerial 404 can be 0.2° C.-in²/W, which is a significant 80% reductionover the thermal resistance of double-sided thermally conductive tape byitself.

FIG. 5 includes a set of six consistent cross-sectional views 502-512illustrating the results of process operations for attaching a heat sinkto a heat-producing electronic device, according to embodimentsconsistent with the figures, particularly FIG. 6.

Views 502-512 illustrate an example process; other views and operationscan be possible. A thermal interface structure formed by these processoperations can be consistent with the cooling apparatuses depicted inFIG. 1-FIG. 4, and can provide an efficient thermal path between aheat-producing electronic device and a heat sink. The process operationsdepicted in FIG. 5 can be used to assemble a cooling apparatus that doesnot require mechanical fasteners to hold the heat sink 116 onto theheat-producing electronic device 114. Such an apparatus can be useful inPCB designs having limited space available for cooling devices such asheat sinks.

The progression depicted in views 502-512 begins with a heat sink 116and a adhesive material 104, view 502, and ends with an assemblyincluding heat-producing electronic device 114, thermally conductivematerial 112, adhesive material 104 and heat sink 116 in view 512.Assembly operations can be completed using commercially availablematerials which can be presently used for thermal interfaceconstruction, such as thermally conductive material 112 and adhesivematerial 104. A thermal interface fabricated using these processoperations can be a particularly useful assembly when incorporatedwithin a high-performance computing device or system.

The results of one or more process operations may be depicted in eachview. For example, a view can depict the results of a materialapplication process, which can include the application of both a tackingadhesive material and a TIM pad. Assembly operations associated withviews 502-512 can include, but are not limited to material alignment,material application, component assembly and affixing operations. Forease of discussion, the views 502-512 depict an adhesive material 104, athermally conductive material 112 and a heat-producing electronic device114 aligned with and assembled onto a heat sink 116. However, it can beunderstood that in some embodiments the adhesive material 104, thermallyconductive material 112, and heat sink 116 can be aligned with andassembled onto heat-producing electronic device 114.

Completed structures may be generally shown in views 502-512 as havingrectangular cross-sectional profiles, with surfaces orthogonal to eachother. This depiction, however, is not limiting; structures can be ofany suitable shape, size and profile, in accordance with specific designcriteria, manufacturing process limitations and available materialprofiles for a given application. For example, corners shown as havingright angles can be rounded, surfaces can have a non-orthogonal relativeorientation, and relative dimensional ratios can vary from thosedepicted in the figures.

The views 502-512 can be useful in illustrating details involved inassembling a thermal interface that has enhanced thermal conductivityrelative to other types of thermal interface structures, while notrequiring the use of external latching hardware to hold a heat sink to aheat-producing electronic device.

View 502 depicts a heat sink 116 and an adhesive material 104 alignedwith edges of the heat sink 116. In some embodiments heat sink 116includes a protrusion 106 extending away from the substantially planarheat sink surface 110 and some embodiments, heat sink 116 has asubstantially planar heat sink surface 110 that does not include aprotrusion 106. Protrusion 106 can be useful for containing a thermallyconductive material or TIM pad within a perimeter formed by protrusion106. According to embodiments, heat sink 116 can include types of heatdissipation devices which can be cooled by dissipating heat into air,refrigerant, water or other fluids. Adhesive material 104 can includecommercially available adhesives such as double-sided adhesive tapes,adhesive material sheets, adhesive liquids, gels, and adhesives inaerosol formulations. According to embodiments, adhesive material 104can have a thickness in a range between 0.05 mm and 1.0 mm. In someembodiments, adhesive material 104 can be thermally conductive, anduseful as a supplemental heat conduction path between the heat sink 116and a heat-producing electronic device 114.

View 504 depicts the results of applying the adhesive material 104 tothe heat sink surface. According to embodiments, adhesive material 104can be a PSA that can be applied to the heat sink surface 110 in a“ring” shape, which can be useful for containing thermally conductivematerial 112. Adhesive material 104 can be applied by processesincluding, but not limited to printing, stenciling, dispensing, e.g.,through a syringe or nozzle, or through an aerosol spray. In someembodiments, adhesive material 104 can be applied in a region thatoverlaps at least one outer edge of a TIM pad, which can be useful infilling gaps between the TIM pad and at least one of the heat sinksurface 110 and the electronic device surface 108. In some embodiments,adhesive material 104 can be useful for, in a subsequent operation,holding or tacking a TIM pad in place during the attachment of the heatsink 116 to the heat-producing electronic device 114. Such tacking canbe useful in preventing damage to a fragile TIM pad during theattachment.

View 506 depicts the results of applying the thermally conductivematerial 112 to the heat sink surface 110. According to embodiments,thermally conductive material 112 can be thermal greases, pastes, gels,curable gels and binders with metal particulates. In some embodiments, aTIM pad, which can include materials such as indium, silver, carbonfiber or various silicone formulations, can be applied either alone orin combination with thermally conductive material 112. In someembodiments, a tacking adhesive material such as transient evaporativematerials, e.g., isopropyl alcohol, or thermally conductive materialsand/or adhesives such as thermal greases, pastes or gels, can be appliedbefore applying the TIM pad, in order to hold the TIM pad in placeduring the assembly process. Application of thermally conductivematerial 112 and/or a TIM pad can be useful in filling gaps between theheat sink 112 and the heat-producing electronic device 114, therebyproviding an enhanced thermal interface.

View 508 depicts a heat-producing electronic device 114 aligned with theheat sink 116. Alignment of heat-producing electronic device 114 withheat sink 116 can be useful for ensuring that thermally conductivematerial 112 is positioned to maintain thermally conductive contact withparticular high thermal output areas of heat-producing electronic device114, to provide efficient heat transfer. In some embodiments,heat-producing electronic device 114 can include a lid 102, in thermallyconductive contact with heat-producing elements, such as ICs, withinheat-producing electronic device 114. In some embodiments,heat-producing electronic device 114 may not include a lid 102; in suchembodiments electronic device surface 108 may include the backside ofone or more IC die.

View 510 depicts the results of assembling the heat-producing electronicdevice 114 to the heat sink 116. According to embodiments, electronicdevice surface 108 of heat-producing electronic device 114 is broughtinto contact with a surface of adhesive material 104. As a result ofthis process, thermally conductive material 112 is brought into contactwith electronic device surface 108, which is useful for establishing anefficient thermally conductive path between the heat-producing electricdevice 114 and the heat sink 116. In some embodiments, thermallyconductive material 112 can also include a TIM pad, possibly inconjunction with thermally conductive material 112.

View 512 depicts the results of affixing the heat-producing electronicdevice 114 to the heat sink 116. According to embodiments, theheat-producing electronic device 114 may be affixed to the heat sink 116by applying a specified compressive force “F1” to the assembly of theheat-producing electronic device 114 and the heat sink 116 for aspecified time. Such a specified compressive force may be useful inactivating an adhesive material 104 that is pressure-sensitive. Forexample, certain PSAs can require an application pressure in a rangebetween 5 psi and 20 psi, for several seconds in order to properlyactivate adhesion.

FIG. 6 is a flow diagram depicting a method 600 for attaching heat sinkto a heat-producing electronic device, according to embodimentsconsistent with the figures, particularly FIG. 5. Method 600 is directedtowards attaching heat sink to a heat-producing electronic devicethrough the use of various combinations of thermally conductive andadhesive materials to achieve an efficient, highly conductive thermalinterface without the use of mechanical latching or attachment hardware.Method 600 can be useful for creating, using commercially availablematerials, a robust, stable and reliable thermal interface particularlysuitable for electronic devices having a high thermal output. Method 600describes series of process operations used to complete the attachmentof a heat sink to a heat-producing electronic device.

Operations depicted and described in FIG. 6 generally correspond to theset of process operations for attaching a heat sink to a heat-producingelectronic device depicted in FIG. 5 and described in the associatedtext. The arrangement of operational blocks within the flow diagram 600of FIG. 6 is not to be construed as limiting the order in which theindividual operations may be performed, as certain embodiments mayperform the operations of FIG. 6 in various alternative orders. For easeof discussion, the operations of method 600 are directed towardsaligning and assembling an adhesive material, a thermally conductivematerial and a heat-producing electronic device onto a heat sink.However, it can be understood that in some embodiments the adhesivematerial, thermally conductive material, and heat sink can be alignedwith and assembled onto heat-producing electronic device.

The process 600 moves from start 602 to operation 604. Operation 604generally refers to aligning an adhesive material to a heat sink.According to embodiments, aligning an adhesive material to a heat sinkcan be useful for ensuring that a thermally conductive materialcontained within a perimeter formed by adhesive material maintainscontact with a specified area of a heat-producing electronic device.Such a specified area can correspond to particularly high thermal outputdevices such as processors or GPUs. In embodiments, the operation ofaligning the adhesive material with the heat sink can be performedmanually or through the use of automated/precision machineryincorporating optical or other types of positioning sensors. Once theadhesive material is aligned, the process moves to operation 606.

Operation 606 generally refers to applying the adhesive material to asurface of the heat sink. According to embodiments, the adhesivematerial can be useful, when applied in a “ring” shape to the heat sinksurface, for containing thermally conductive material and/or TIM pad ina specified location. Such containment can provide an optimized,efficient cooling path for the heat-producing electronic device. Inembodiments, the adhesive material can be a PSA. Once the adhesivematerial is applied, the process moves to operation 608.

Operation 608 generally refers to applying a thermally conductivematerial to the surface that the adhesive material is applied to.According to embodiments, thermally conductive material 112 can beapplied through printing, stenciling, dispensing, e.g., through asyringe or nozzle. Thermally conductive material 112 can be useful forfilling gaps between the heat sink 112 and the heat-producing electronicdevice 114, thereby providing an enhanced thermal interface. Once thethermally conductive material is applied, the process moves to operation610.

Operation 610 generally refers to aligning the heat-producing electronicdevice to the heat sink. According to embodiments, alignment of theheat-producing electronic device with the heat sink can be useful forensuring that thermally conductive material is positioned to maintainthermally conductive contact with particular areas of the heatheat-producing electronic device, in order to provide efficient heattransfer from the electronic device to the heat sink.

In embodiments, the operation of aligning the heat-producing electronicdevice 114 with heat sink 116 can be performed manually or through theuse of automated/precision machinery incorporating optical or othertypes of positioning sensors. Once the heat-producing electronic deviceis aligned to the heat sink, the process moves to operation 612.

Operation 612 generally refers to assembling the heat sink to theheat-producing electronic device. According to embodiments, a portion ofthe surface of the heat-producing electronic device is brought intocontact with the adhesive material while another portion of theheat-producing electronic device surface is brought into contact withthe thermally conductive material. Establishing such contact is usefulto cause adhesion between the adhesive material and the heat-producingelectronic device and to establish an efficient, thermally conductivecontact between the thermally conductive material and the electronicdevice. Once the heat sink is assembled to the heat-producing electronicdevice, the process moves to operation 614.

Operation 614 generally refers to the affixing the heat sink to theheat-producing electronic device. According to embodiments, theheat-producing electronic device may be affixed to the heat sink byapplying a specified compressive force to the assembly of theheat-producing electronic device and the heat sink for a specified time.Such a specified compressive force may be useful in activating anadhesive material that is pressure-sensitive. Both the magnitude andtime duration of the compressive force may be monitored and controlledmanually or through the use of automated equipment. Once heat sink isaffixed to the heat-producing electronic device, the process 600 may endat block 616.

The descriptions of the various embodiments of the present disclosurehave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A method for attaching a heat sink to aheat-producing electronic device, one of the heat sink and theheat-producing electronic device having a first surface, the other ofthe heat sink and the heat-producing electronic device having a secondsurface, the heat sink including a protrusion extending away from theheat sink, the method comprising: aligning an adhesive material to thefirst surface; applying the adhesive material to the first surface toform an outer perimeter; applying, within the outer perimeter, athermally conductive material to the first surface, the thermallyconductive material contained within spatial confines defined by theouter perimeter, the first surface, and the second surface; aligning thesecond surface to the first surface; assembling the heat sink to theheat-producing electronic device by bringing the second surface intocontact with the adhesive material; and affixing the heat sink to theheat-producing electronic device by applying a compressive force to theheat sink and to the heat-producing electronic device, the compressiveforce activating the adhesive material.
 2. The method of claim 1,wherein the adhesive material is a pressure-sensitive adhesive (PSA)selected from the group consisting of a double-sided adhesive tape, anadhesive material sheet, an adhesive gel, a curable adhesive and anaerosol adhesive.
 3. The method of claim 1, wherein the applying of thethermally conductive material to the first surface includes applying athermal interface material (TIM) pad to the first surface.
 4. The methodof claim 1, wherein the applying of the thermally conductive material tothe first surface includes an application, to the first surface, of atacking material configured to hold a thermal interface material (TIM)pad adjacent to the first surface during assembly of the heat sink tothe heat-producing electronic device.
 5. The method of claim 1, whereinthe adhesive material holds a thermal interface material (TIM) padadjacent to at least one of the first surface and the second surface. 6.The method of claim 5, wherein the adhesive material is thermallyconductive and fills at least one gap between the TIM pad and the atleast one of the first surface and the second surface to which the TIMpad is held adjacent.
 7. The method of claim 1, wherein the applying ofa thermally conductive material to the first surface includes anapplication of a formable thermal conductive material selected from thegroup consisting of a thermal grease, a thermal paste, a thermal gel anda phase-change material.
 8. The method of claim 1, wherein the affixingof the heat sink to the heat-producing electronic device includes anadhesive material curing process.
 9. The method of claim 8, wherein theadhesive material curing process causes a contraction of the adhesivematerial, the contraction providing a tensile force between the firstsurface and the second surface.
 10. The method of claim 1, wherein, onceactivated, the adhesive material holds the first surface in an adjacent,coplanar orientation to the second surface such that an outer cavity isformed, wherein the outer cavity is bounded by the outer perimeter, thefirst surface and the second surface, wherein a thermally conductivematerial is contained in an inner cavity enclosed within the outercavity, the inner cavity bounded by an inner perimeter, the firstsurface and the second surface, and wherein the thermally conductivematerial is configured to cool the heat-producing electronic device byproviding a thermally conductive path between the first surface and thesecond surface.
 11. The method of claim 10, wherein the first surfacehas a protrusion extending away from the first surface, the protrusiondefining the inner perimeter on the first surface.
 12. The method ofclaim 11, wherein a first height of the protrusion, extending away fromthe first surface, is in a range between 40% and 90% of a second heightof the adhesive material.
 13. The method of claim 11, wherein an outlineof the adhesive material defines a vent formed between the innerperimeter and an exterior perimeter of the adhesive material.
 14. Themethod of claim 1, wherein a first height of the protrusion, extendingaway from the heat sink, is in a range between 40% and 90% of a secondheight of the adhesive material.
 15. The method of claim 1, wherein afirst height of the protrusion, extending away from the heat sink, isless than a distance, in an assembled configuration, between the firstsurface and the second surface.
 16. The method of claim 1, wherein theadhesive material is thermally conductive and configured to transferheat between the second surface and the first surface.
 17. The method ofclaim 1, wherein the adhesive material is chemically inert with respectto the thermally conductive material.
 18. The method of claim 1, whereinan outline of the adhesive material defines a vent formed between thespatial confines defined by the outer perimeter and an exteriorperimeter of the adhesive material.
 19. The method of claim 1, wherein athermally conductive material is positioned, in an unassembledconfiguration, at a perimeter of a thermal interface material (TIM) pad,the TIM pad located within the spatial confines defined by the outerperimeter, the first surface, and the second surface, the thermallyconductive material positioned, in an assembled configuration, betweenthe TIM pad and at least one of a portion of the first surface and aportion of the second surface.
 20. The method of claim 19, wherein theadhesive material is thermally conductive and is positioned, in theassembled configuration, between the TIM pad and at least one of aportion of the first surface and a portion of the second surface.